The present invention relates to the technology to control a sound quality in employing external speakers.
During watching television, a user of a television set listens to sounds from built-in speakers of the television set or headphones. At this time, when the sounds are emitted from the built-in speakers of the television set and the sounds are emitted from the headphones, respective frequency characteristics of the built-in speakers of the television set and the headphones are different. Therefore, when the built-in speakers and the headphones are switched in use, there exists the technology to correct frequency characteristics of audio signals in response to respective frequency characteristics and then emit the sounds (Patent Literature 1, for example).    [Patent Literature 1] JP-A-2004-64172
Meanwhile, nowadays a flat large-screen television set such as a liquid crystal display, or the like is becoming the mainstream of the television set, and the slimming down and the larger screen are advancing year by year. Since such a design is employed that an area of a display screen is increased in size in contrast to the housing of the television set, the narrower frame is also advancing. The internal speakers being arranged in the frame position up to now must be reduced in size correspondingly, and thus a tone quality becomes worse. In this situation, when the user of such television set cannot be satisfied with this tone quality, such user often watches the television while using the speaker unit of the high tone quality provided to the outside. Also, the user provides plural types of speaker units, and then uses an adequate speaker unit individually to suit the listening contents.
Here, in the technology disclosed in Patent Literature 1, even when the type of the headphones connected to the television set is changed, the corrected contents of the frequency characteristic of the audio signal are not changed, but the desired sound can be emitted because the frequency characteristic of the headphones is not so largely changed. In contrast, when not the headphones but the speaker units are employed, the frequency characteristic is often largely different depending on the type. However, in the television set using the technology disclosed in Patent Literature 1, even when the type of the speaker units connected to the television set is changed, the corrected contents of the frequency characteristic of the audio signal are never changed, so that the desired sound cannot be emitted.
In this manner, the speaker units connected externally often have various frequency characteristics in simply emitting the sound depending on the type. Therefore, a tone quality controlling circuit for correcting the audio signal must be provided to get the desired frequency characteristic, which acts as a factor of high cost. Also, when the speaker unit is built in the television stand, a load on the tone quality controlling circuit can be reduced by devising a layout of the speakers whereas a margin of an outside design is restricted on account of a limitation on the layout of the speakers.